Alarm systems are known in which the sensors disposed at desired positions in a protected facility are in wireless communication with a central unit at the facility, each sensor location including a radio frequency (RF) transmitter which provides a coded transmission representing the status or alarm condition of the associated sensor. The transmission from each sensor is received and decoded by a receiver at the control unit to provide an output indication of status or alarm condition.
During installation of the sensor transmitters, and during testing of the sensor transmitters, it is important to measure the signal strength of the RF signal as received at the control unit. The control unit is usually remote from the sensor locations, and visual indications of signal strength at the control unit cannot be seen by installation or test personnel at the transmitter locations. There have been proposals for providing an audible indication at the control unit or signal strength, but the proposed techniques have not provided the convenience and accuracy necessary for ascertaining transmission strength margin and actual performance of the various transmitters in the system. One known test arrangement is employed in the CS-200 alarm system of Aritech Coporation in which an audible tone is produced at a control panel in response to activation of any sensor of the system.
The tone indicates that a sensor has been activated, but no measure of signal strength nor the ability to estimate signal margin is provided.
An alarm system of Alarm Device Manufacturing Co. has a test system which measures received signal strength and retransmits a signal in the FM broadcast band which is compsoed of a sequence of up to three tones, which provides a rough indication of signal strength, and no actual measure of received signal strength. This technique requires extra equipment for retransmitting the signal in the FM broadcast band and an FM receiver for receiving the retransmitted signal, and also requires the selection of a clear channel in the FM band.